Seoul’s submarine scenarios
South Korea is currently in final negotiations with the United States on a deal that could reshape the balance of power in the Indo-Pacific: the construction of nuclear-powered submarines. What began as a diplomatic coup — Washington’s agreement in principle to support Seoul’s acquisition — has become bogged down in one deceptively simple question: where will they be built?
The still unresolved decision carries implications not only for the Korean Peninsula but also for the AUKUS submarine pact, Australia’s long-term naval strategy, and the future of the ROKUS alliance. Four scenarios stand out, each revealing a different trajectory for how U.S. allies will cooperate into the future.
Four sub scenarios
American built? In the first scenario, Korea’s nuclear submarines are built in U.S. shipyards. At first glance, that sounds like a win for American industry and political optics — the very point of Donald Trump’s recent declaration that construction should occur at Philadelphia’s Hanwha-owned yard. Yet U.S. facilities are already way overstretched. The American submarine industrial base is divided between two main yards in Groton (Connecticut) and Newport News (Virginia). Both are struggling to meet existing commitments for Virginia-class and Columbia-class boats. Adding Korea to that queue would likely delay every project downstream, including Australia’s AUKUS ambitions.
In short, if Korea’s submarines are built in the U.S., America’s yards would need to expand dramatically — and the much-promised AUKUS timeline for Australia’s first nuclear submarine would slip even further into the 2040s. Importantly, it would also take away the potential for an all important Plan C (see below) if and when AUKUS falls apart like a Trump 47 commemorative desk gadget.
American built with Korean help? A second, more optimistic interpretation sees opportunity in the same scenario. Hanwha’s acquisition of the Philadelphia shipyard and its $5 billion investment promise the chance to expand U.S. production capacity. Korea could effectively help rebuild the U.S. industrial base, supplying trained workers, modular construction technology, and systems integration know-how gained from decades of building advanced diesel-electric boats. The result could be an “AUKUS plus” model — Korea helping to clear the U.S. backlog while deepening interoperability with both the U.S. and Australia.
But this version of cooperation requires long-term political commitment and bureaucratic imagination — two things in short supply. It would also take time. The U.S. Department of Energy, not the Pentagon, currently holds review authority for Korea’s use of enriched uranium fuel, and it is considering the issue narrowly through a regulatory lens, not an alliance one. Without a White House-level push to integrate defense industrial cooperation, Korea’s shipbuilding potential could remain stranded in Philadelphia’s dry docks.
AUKUS Plus? The third scenario would bring Korea directly into the AUKUS framework. Strategically, this makes sense: A trilateral alliance that already spans the Atlantic and the Pacific could benefit enormously from Korean shipbuilding skill and technological sophistication. An AUKUS Plus model would distribute submarine production more efficiently — and overcome the weaknesses in British and U.S. production.
Significantly, such a scenario would also tie South Korea into the broader U.S. alliance framework, removing rapidly emerging doubts and concerns that Seoul is being set up to be a frontline patsy in the global U.S.-China competition. South Korea is rapidly securing an independent capacity and has over the past decade strengthened its naval, industrial arms, satellite intelligence collection, and missile range and payload capacities. For some, this opens Seoul to a new, more independent path. Fitting South Korea into AUKUS Plus would largely negate this path.
Yet such a vision requires serious strategic thought and political will. Washington would need to open what has always been a jealously guarded sphere of nuclear cooperation. Even under AUKUS, the United States shares little of its reactor technology, and congressional oversight remains intense. Korea’s involvement would also force a rethink of export-control regimes and fuel agreements, given that the 2015 Korea-U.S. nuclear accord forbids the military use of enriched uranium. Amending that deal would be politically treacherous in Washington and symbolically sensitive in Seoul.
For now, this scenario seems remote — not because it lacks logic, but because it demands the kind of alliance innovation that current policymakers in Washington are ill-suited to deliver.
An Australian Plan C? The final, and perhaps most intriguing, scenario is that Korea builds its nuclear submarines at home. Seoul’s shipyards are among the most advanced in the world, and Korean engineers have accumulated decades of experience constructing diesel-electric submarines for both domestic use and export. If Korea successfully develops a small modular reactor suitable for naval propulsion — a goal now aligned with its civilian SMR program — it could complete the circle: full-spectrum indigenous capability.
In that event, Australia may find its long-term “Plan B” through the U.K.-U.S. AUKUS pathway overshadowed by a “Plan C”: Korean-built nuclear submarines that arrive earlier, cost less, and carry fewer political strings. Such a shift would profoundly reshape regional industrial alignments.
Canberra’s obsession with AUKUS timelines and Anglo-American transfer mechanisms might look increasingly dated in a region where Korea is building and exporting nuclear propulsion before Australia even lays its first keel. But this would never sail in Australia. Politically, going from Japan to France to AUKUS and onto Korea with submarines forever receding into the future to a point in time when they’ll probably be technologically redundant, would pretty much confirm to everyone that internally the government is as feckless as it looks from the outside.
A different Korea?
The fact that South Korea is negotiating the deal should be a wake up call to the U.S. South Korea’s position in this debate will soon no longer be that of a dependent junior partner waiting for Washington’s permission.
The negotiations over nuclear submarine construction reveal something deeper — a country that has, quietly and deliberately, built the foundations of strategic autonomy. Seoul’s shipbuilding capacity is only one part of a much wider transformation. Over the past decade, South Korea has strengthened its naval reach, expanded missile range and payloads, established advanced satellite intelligence collection, and integrated defense industries capable of competing with Europe’s mid-tier arms producers.
What this means is that the logic of dependence that once governed the Korea–U.S. alliance is breaking down. Nuclear submarine construction, whether in Groton, Philadelphia, or Ulsan, will no longer simply reflect American generosity but rather how Washington chooses to manage a partner that is rapidly becoming too capable to be treated as subordinate.
For Seoul, the nuclear submarine debate is as much about political symbolism as naval engineering — it tests how far Korea can act as a technological equal within an alliance still framed by hierarchy.
For some in Seoul, that opens the door to a new path: one of selective independence, balancing between alliance reassurance and sovereign capability. A Korean-built nuclear submarine would be the culmination of that long process — the moment when the Republic of Korea finally joins the narrow circle of nations that can operate below the waves without anyone else’s approval.
It’s in America’s interests to envision the future of the ROKUS alliance as it decides which submarine scenario makes the most sense. If handled poorly, jobs today may mean a weaker alliance in the future.
